(1) Field of the Invention
The present invention relates to a thermal printer comprising a plurality of thermal heads arranged around a platen roller for carrying out a printing operation by heating the thermal heads to transfer thermally fusible or sublimable ink onto recording paper. In particular, the invention relates to a thermal printer used for multicolor recording such as color printing.
(2) Description of the Prior Art
A thermal printer having a plurality of thermal heads around a platen roller is known as a multihead thermal printer. Different color ink films are provided for the respective thermal heads. The ink films are superposed on recording paper, the thermal heads are pressed against the ink films, and pulses are applied to the thermal heads, whereby inks are selectively fused to effect printing on the recording paper. An image having a selected color tone is formed on the recording paper in a single color or in a combination of colors with the plurality of inks transferred individually or in superposition. The ink films are fed by an ink film feed mechanism to supply the respective thermal heads with different colors. It is necessary to monitor unused amounts of the ink films since the ink films are finite and, after one of the ink films is used up, further printing is of no use. To meet this requirement it is conceivable to provide the multihead thermal printer with an ink film used with a single-head thermal printer and having an end mark at a trailing end thereof, and to detect consumption of the ink film by means of the end mark. Aside from the case in which the end mark is detected when one sheet has just been printed in a single-sheet printing, in other cases there is the problem of the sheet being wasted even if 90% (for example) of printing on that sheet is completed, since the printing operation is discontinued upon detection of the end mark. A large amount of recording paper may be wasted when the end mark is detected in the middle of a continuous printing operation.